1. Field of the Invention
The present invention relates to a laser controller and, more particularly, to a laser light amount controller which can adjust the amount of light from a light source used in a recording apparatus, independently of the detection output of a light detector and to a laser light monitoring method.
2. Description of the Related Art
A data recording apparatus for recording data by irradiating light on a recording medium uses, for example, a semiconductor laser as a light source. Normally, a light receiving element (photodiode) receives the output of the semiconductor laser so as to detect the amount of light from the semiconductor laser. A laser controller controls the output of the semiconductor laser in accordance with the detected amount of light in order to keep the amount of light from the semiconductor laser constant.
It is known that semiconductor lasers and light receiving elements generally have a variation in operational point, the level of the maximum point being three to five times greater than that of the minimum point. To cope with this problem, a laser controller is provided with a variable power source for varying the operational point to provide the proper laser output. Such a laser controller is described in U.S. Pat. No. 4,516,242.
From the view point of circuit design, however, such a variable power source cannot independently adjust the variation in output of the light receiving element and the variation in output of the semiconductor laser. In other words, varying the output of the light receiving element changes the threshold value of the laser light accordingly. Naturally, an adjusted output of the light receiving element does not necessarily correspond to the output of the semiconductor laser.
The laser controller generally has a circuit for generating a ready signal that indicates the irradiation of laser light and a circuit for generating an alarm signal that indicates abnormal irradiation of laser light. Since the output of the light receiving element does not necessarily correspond to the output of the semiconductor laser, the alarm signal may be generated even when the irradiation of laser light is not abnormal, or, in some cases, when abnormal irradiation of laser light occurs, it is not correctly transferred to the light receiving element. In the latter case, no alarm signal would be generated and the abnormal irradiation cannot be stopped, which may damage a recording film on a recording medium.